Electrochemical gas sensors are suitable for detecting chemical components in gases. Possible uses of gas sensors according to the present invention are found in fields of use of conventional electrochemical gas sensors as well as in fields of use in which the use of such sensors has not hitherto been possible for reasons related to size.
Due to their principle of action, electrochemical gas sensors contain a plurality of electrodes, which communicate with one another via an electrolyte. The arrangements used most commonly comprise a working electrode and a counterelectrode or a working electrode and a counterelectrode, with which a reference electrode is associated.
Electrochemical gas sensors currently comprise usually a large number of components, which are arranged piece by piece in mostly injection-molded plastic housings in a plurality of operations. Among other things, the above-mentioned electrodes, which are wetted by electrolyte at least on one side and are often even completely enclosed by electrolyte, are arranged in the housing. Due to the relatively large minimum electrolyte volume needed to wet all electrodes and the hygroscopic properties of most electrolytes, a large compensation volume must be provided in the prior-art designs in order to cover the broadest possible range of environmental humidity levels and to prevent as a result the sensor from bursting or drying out. Requirements applicable to the height and a minimum volume of prior-art sensor designs arise from the requirements imposed on the electrolyte volume as well as other general design conditions concerning the assembly of a plurality of components. Thus, the size of these sensors hinders the further spread of the use of electrochemical gas sensors despite the possibility of the adequately reproducible measurement of a great variety of gas components.
Another drawback of prior-art electrochemical gas sensors is the great effort that is needed for their assembly.
It is known from DE 195 47 150 A1 that the volume of an electrochemical gas sensor can be reduced by using as the electrolyte volume the volume of electrolyte that can be placed into a planar electrolyte carrier. The electrodes necessary for the ability of the electrochemical gas sensor to function are arranged around the electrolyte carrier. These are covered by gas-permeable membranes. The sandwich-like arrangement is surrounded by a planar upper part and lower part, which form a housing. It is explicitly stated here that strength is imparted to the housing by a circumferential frame. The relatively complicated structure of the housing remains as a possibly limiting drawback in the above-described embodiment.
It is, furthermore, known that a pocket structure, which accommodates the corresponding sensor components, can be formed by the frameless connection of the approximately planar upper and lower parts (EP 1 413 881 A2). The drawback of the solution being presented here is, however, that the electrodes are contacted by the connection area between the housing parts. Even though the structure of the initial porous contact material is changed during the connection of the housing parts such that the diffusion of the electrolyte is greatly reduced, experience has shown that it is not possible to find a solution that would be stable over the long term in this manner.